arm64/debug: Eliminate magic number for size of BRK instruction

The size of an A64 BRK instruction is the same as the size of all other
A64 instructions, because all A64 instructions are the same size.

BREAK_INSTR_SIZE is retained for readibility, but it should not be
an independent constant from AARCH64_INSN_SIZE.
Signed-off-by: Dave Martin <Dave.Martin@arm.com>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Will Deacon <will.deacon@arm.com>

arch/arm64/include/asm/debug-monitors.h

@@ -18,6 +18,8 @@
 
 #ifdef __KERNEL__
 
+#include <asm/insn.h>
+
 /* Low-level stepping controls. */
 #define DBG_MDSCR_SS		(1 << 0)
 #define DBG_SPSR_SS		(1 << 21)
@@ -38,7 +40,7 @@
 /*
  * Break point instruction encoding
  */
-#define BREAK_INSTR_SIZE		4
+#define BREAK_INSTR_SIZE		AARCH64_INSN_SIZE
 
 /*
  * ESR values expected for dynamic and compile time BRK instruction